- Email: [email protected]
Radiation induced nucleation of nanoparticles in silica
Nuclear Instruments and Methods in Physics Research B 166±167 (2000) 845±850
www.elsevier.nl/locate/nimb
Radiation induced nucleation of nanoparticles in silica q D. Ila a
a,*
, E.K. Williams a, R.L. Zimmerman a, D.B. Poker b, D.K. Hensley
b
Department of Naur. and Phys. Sciences, Center for Irradiation of Materials, Alabama A&M University, P.O. Box 1447, Normal, AL 35762-1447, USA b Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Abstract There is a threshold implantation dose, after which some of the implanted species will tend to spontaneously form nanoclusters, over-dose-implantation. Similarly, there is a threshold implantation dose for the implanted species in a layer of the host material, such that after high temperature annealing the nanoclusters can nucleate before the implanted material can dissolve in the host material (during such heat treatments). In this paper, we present the results of our investigation of producing nanoclusters of gold in silica at ¯uences of two orders of magnitude less than what is traditionally used. This is accomplished by implanting 2.0 MeV Au into silica followed by MeV bombardment by MeV Si ions. This process was used to reduce the threshold implantation dose by at least two orders of magnitude. To follow the formation of nanoclusters, we used both indirect measurement methods such as optical absorption spectrophotometry (non-destructive), and direct methods such as transmission electron microscopy (destructive). The size of the nanoclusters, ranging from 1 to 10 nm, are controlled by the implantation dose and by the total electronic energy deposited by each post-bombarding ion in the implanted layer. We will show how and at what concentrations species such as gold nucleates to form nanoclusters, either by induced strain or by radiation-enhanced nucleation at a dose below that needed for spontaneous nanocluster formation. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 61.72. Ww; 61.82.Rx; 42.70.Nq Keywords: Ion implantation; Nanocrystals; Optical materials
1. Introduction
q Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and the Division of Materials Sciences, US Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp. * Corresponding author. Tel.: +1-256-851-5866; fax +1-256851-5868. E-mail address: [email protected] (D. Ila).
The production of the variety of optical devices relied mostly on changes in both the linear and nonlinear properties of glasses. The traditional technique to change the linear properties of glasses has been mostly by melting selected metals with glass, cooling the melt to form homogeneous glass, and then forming the metal colloids by a reheating process. Recently, metallic ion implantation in addition to thermal annealing has been used to
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 7 9 4 - 6
846
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
introduce similar eects near the surface as well as nonlinear optical properties [1±8]. The techniques used to form nanoclusters may be categorized as follows: 1. room temperature implantation followed by high temperature annealing; 2. room temperature implantation at dosage above the threshold dose for spontaneous nanocluster formation; 3. ion implantation at elevated temperatures. An attractive property of ion implantation is that the ions can be focused to introduce the linear and nonlinear properties in a well-de®ned space in an optical device. In all of the above cases, to produce nanoclusters of implanted ions such as gold in a medium such as silica, the implantations were done at high doses, from 1 to 2 ´ 1017 ions/cm2 , to overcome the solubility of the implanted species into the substrate. That is also why there is a wide distribution of cluster sizes produced by the above techniques. To overcome this problem, since 1994, we initiated a series of investigations into how to con®ne the implanted ions in a narrow layer, by generating chemical barriers, engineering defect barriers on both sides of the implanted layer, as well as combining two nonequilibrium processes, ion implantation and post-irradiation [9,10]. The latter technique, the focus of this paper, has been a combination of implantation of metallic species at room temperature, followed by room temperature bombardment by mega-electron-volt ions. The result has been the production of nanoclusters of gold in silica at ¯uences as low as 5 ´ 1015 / cm2 , a ®ne control in the size of the nanoclusters, and production of more uniform size nanoclusters. In this paper, we report on the synthesis of Au nanoclusters in silica (Suprasil 300) by combining two nonequilibrium techniques, consisting of implantation of 2.0 MeV Au and post-implantation bombardment with a 5.0 MeV Si beam. The formation of Au nanoclusters was investigated using optical absorption photospectrometry (OAP) techniques, following the formation of optical absorption bands due to formation of Au nanocrystals. The structure, shape, size and location of these nanoclusters were studied using cross-sec-
tional transmission electron spectroscopy (TEM) as well as electron diraction. 2. Experimental procedures The silica glass used is suprasil-300 of known purity, 5 ´ 5 ´ 0.5 mm3 , a commercial product of Heraeus Amersil, Gold ions at 2.0 MeV were implanted at low current density of 2 lA/cm2 to produce a Au implanted layer at concentrations between 5 ´ 1015 /cm2 and 1.2 ´ 1017 /cm2 . The beam current was maintained low to avoid the premature formation of gold clusters due to the ion beam heating. The depth of the implanted layer, 0.48 lm, as well as the penetration range of the postbombarding particles were calculated using the TRIM [11] computer code and measured using the RBS technique. The energy of the bombarding Si particles, 5.0 MeV, was selected such that Si ions stop outside the range of the Au implanted layer and at ¯uences between 6 1016 /cm2 and 2 1017 / cm2 . In all of the above post-implantation bombardments the temperature of the suprasil was kept at room temperature, 300 K. The OAP for small nanoclusters formed due to ultra-low dose implantation was measured by subtracting the OAP for Si bombarded suprasil and the OAP for Au implanted suprasil. This was done using two techiques: (1) during the OAP measurement of the Au implanted and then Si bombarded suprasil, (2) after the OAP measurements were done for Au implanted and then Si bombarded suprasil, for Si bombarded suprasil, and for Au implanted suprasil, then subtracting the normalized spectra for Si bombarded and Au implanted from the OAP spectrum for Au implanted and Si bombarded suprasil. Both of these techniques produce similar results. 3. Results and discussion The higher the ion beam ¯uence and the higher the atomic number of the bombarding ion the more the damage to the silica glass resulting in a change of the optical properties [7,12,13]. This was observed by absorption spectrometry during all
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
847
Fig. 1. From left to right, TEM micrographs of suprasil implanted at room temperature with (A) 2.0 MeV Au at 1:2 1017 =cm2 then annealed at 1173 K, the line on the top is the surface of the suprasil, (B) 2.0 MeV Au implanted suprasil at 6 1016 =cm2 then bombarded by 5.0 MeV Si at 6 1016 =cm2 , the image is taken from the implanted layer, (C) 2.0 MeV Au implanted suprasil at 5 1015 =cm2 then bombarded by 5.0 MeV Si at 6 1016 =cm2 , the image is from the implanted layer.
bombardments, but these eects are reduced with heat treatments above 970 K [7,8]. Fig. 1, from left to right, shows comparison of TEM micrographs of suprasil implanted at room temperature with 2.0 MeV Au at 1:2 1017 /cm2 then annealed at 1173 K with a 2.0 MeV Au implanted suprasil at 6 1016 /cm2 then bombarded by 5.0 MeV Si at 6 1016 /cm2 and the far right micrograph is the Au implanted suprasil at 5 1015 /cm2 then bombarded by 5.0 MeV Si at 6 1016 /cm2 . The 1173 K annealed Au implanted suprasil shows various size Au nanoclusters spread from the implantation range towards the surface. The micrographs from the post-implantation Si bombarded Au implanted suprasil show almost uniform size Au nanoclussters. The middle micrograph shows 2±3 nm size Au nanoclusters for 2.0 MeV Au implanted suprasil at 6 1016 /cm2 . The right micrograph shows sub-nanometer size Au nanoclusters 2.0 MeV Au implanted suprasil at 5 1015 /cm2 . Fig. 2 shows the optical absorption spectra bands for the 2.0 MeV Au implanted suprasil at 6 1016 /cm2 after bombardment by 5 Mev Si at 6 1016 /cm2 , 8 1016 /cm2 , 1 1017 /cm2 , and 2 1017 /cm2 at room temperature. As it is shown in this ®gure, the more the post-implanatation Si bombardment does the more pronounced the observed optical absorption band at about the cal-
Fig. 2. The optical absorption spectra of four suprasil samples ®rst implanted with 2.0 MeV Au at a ¯uence of 6 1016 =cm2 then each bombarded by 5 MeV Si at the ¯uences shown at room temperature.
culated wavelength using the Mie theory [14], 520 nm. The further post-implantation bombardment at room temperature, 2 1017 /cm2 , increases the
848
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
absorption coecient at higher Si implantation dose [15], as indicated by an increase in the background, considering the absorption due to implanted Si as background base line in this optical measurement. Fig. 3 shows the optical absorption spectra band from suprasil implanted with 1:2 1017 /cm2 Au at 2.0 Mev after annealing at 1273 K as well as suprasil implanted with 6 1016 /cm2 Au at 2.0 Mev and post-bombarded by 5.0 Mev Si at 6 1016 /cm2 , 8 1016 /cm2 , 1 1017 /cm2 , and 2 1017 /cm2 all were annealed at 1273 K. Comparing the absorption spectra band due to formation of Au nanoclusters obtained from heat treated Au implanted silica, 525 nm, and the absorption band due to Au nanoclusters, 517±520 nm, for post-implantation Si bombarded silica indicates 5±10 nm blue-shift which could be due to the change in the linear optical properties of the Si bombarded silica. Even after heat treatment at 1273 K the intensity of the absorption band for Si bombarded samples are similar to those from Fig. 2. The only dierence is the position of the ab-
Fig. 3. The optical absorption spectra for ®ve 1273 K annealed suprasil samples, one implanted with 1:2 1017 =cm2 Au only and the four Si bombarded samples shown in Fig. 2.
Fig. 4. The optical absorption band for 2.0 MeV Au implanted at 5 1015 =cm2 and then bombarded by 5.0 MeV Si at 6 1016 =cm2 at room temperature.
sorption band is slightly red shifted, which is due to thermal relaxation of the Si bombarded suprasil, thus recovering its original index of refraction value. Fig. 4 shows the optical absorption spectra bands for the 2.0 Mev Au implanted suprasil at 5 1015 /cm2 samples after bombardment by 5 Mev Si at 6 1016 /cm2 at room temperature. This ®gure corresponds to the far right TEM micrograph in Fig. 1 and is obtained by a background base-line subtraction of linear optical eect due to Si bombardment as well as due to Au implantation before Si bombardment. Table 1 shows the energy deposited by the electronic excitations (ee ), by nuclear stopping (en ), and integral of the product of the extinction coef®cient and the wavelength [10,14] at the absorption band after post-implantation bombardment by Si beam at 1.2, 2.0, and 5.0 MeV. The energy deposited at the Au implanted layer is calculated using TRIM computer code [11]. In this table the ex-
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850 Table 1 Energy deposited in the gold implanted layer and the product of extinction coecient and the wavelength for each incident energy Si beam energy (MeV)
DE (eV) due to ee
DE (eV) due to em
ak (nm)
1.2 2 5
107 017 176 868 373 018
6976 4814 2980
4.1 8.6 27
tinction coecient (a) is normalized and arbitrary unit. To evaluate the mechanism by which the nanoclusters are formed using post-implantation bombardment, we implanted gold and silicon at energies such that their implantation range were the same. We implanted 5.5 MeV Au ions at similar concentrations as above, 1.4 um implantation range, followed by 1.0 MeV Si ion bombardment at various ¯uences, 1.4 um implantation range produced no Au nanocluster. This recon®rms that the process of nanocluster formation is mostly due to the electronic energy deposited by the MeV Si ions passing through the Au implanted layer and not due to the nuclear stopping eects.
849
better control in their size distribution at much lower implantation dosage is to combine the ion implantation with a post-mega-electron-volt ion bombardment. The combined two nonequilibrium techniques can induce the formation of Au nanoclusters with ®ne control on the size of the nanoclusters, ranging from 0.5 to several nanometers depending on the combination of implanted dosage and the electronic energy deposited per postimplantation bombarding ions, thus generating an optical absorption band at about 520 nm and third order nonlinearity in a more con®ned volume.
Acknowledgements This project was supported by the Center for Irradiation of Materials at Alabama A&M University and Alabama EPSCoR-NSF Grant No. OSR-9559480. The work at ORNL was sponsored by the Division of Material Sciences, US Department of Energy, under Contract DE-ACO596OR22464 with Lockheed Martin Energy Research Corp.
References 4. Conclusion Comparing the area under the absorption band for constant ¯uence Si bombardment at dierent energies to the electronic energy deposited at the Au implanted depth, indicates similar increasing trend. Meanwhile, the energy deposited due to the nuclear stopping power of Si ions at dierent energies, in the Au implanted layer, shows just the opposite trend. The energy deposited by electronic excitations by MeV Si in the Au implanted layer contributes to both formation of large size nanoclusters and to an increase of the nanoclusterÕs volume fraction. That is, why the integral under the absorption band is increasing faster than the increase in the electronic energy deposited by Si ions at higher energies. The solution to produce a more con®ned metallic nanoclusters in any host material with a
[1] G.W. Arnold, J. Appl. Phys. 46 (1975) 4466. [2] G.W. Arnold, J.A. Bordes, J. Appl. Phys. 48 (1977) 1488. [3] R.H. Margruder III, R.A. Zuhr, D.H. Osborne Jr, Nucl. Instr. and Meth. B 99 (1995) 590. [4] R.F. Haglund Jr., D.H. Osborne Jr., R.H. Magruder III, C.W. White, R.A. Zuhr, P.D. Townsend, D.E. Hole, R.E. Leuchtner, Mat. Res. Soc. Symp. Proc. 354 (1995) 629. [5] C.W. White, D.S. Zhou, J.D. Budai, R.A. Zuhr, R.H. Magruder, D.H. Osborne, Mat. Res. Soc. Symp. Proc. 316 (1994) 499. [6] K. Fukumi, A. Chayahara, M. Adachi, K. Kadono, T. Sakaguchi, M. Miya, Y. Horino, N. Kitamura, J. Hayakawa, H. Yamashita, K. Fujii, M. Satou, Mat. Res. Soc. Symp. Proc. 235 (1992) 389. [7] D. Ila, Z. Wu, R.L. Zimmerman, S. Sarkisov, C.C. Smith, D.B. Poker, D.K. Hensley, Mat. Res. Soc. Symp. Proc. 457 (1997) 143. [8] D. Ila, E.K. Williams, S. Sarkisov, C.C. Smith, D.B. Poker, D.K. Hensley, Nucl. Instr. and Meth. B 141 (1998) 289.
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[9] D. Ila, Z. Wu, C.C. Smith, D.B. Poker, D.K. Hensley, C. Klatt, S. Kalbitzer, Nucl. Instr. and Meth. B 127 (1997) 570. [10] D. Ila, E.K. Williams, C.C. Smith, D.B. Poker, D.K. Hensley, C. Klatt, S. Kalbitzer, Nucl. Instr. and Meth B 148 (1999) 1012. [11] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985.
[12] E.R. Schineller, R.P. Flam, D.W. Wilmot, J. Opt. Soc. Am. 58 (1968) 1171. [13] P.D. Townsend, Nucl. Instr. and Meth. B 46 (1990) 18. [14] G. Mie, Ann. Physik. 25 (1908) 377. [15] M. Verhaegen, L.B. Allard, J.L. Brebner, M. Essid, S. Roorda, J. Albert, Nucl. Instr. and Meth. B 106 (1995) 438.
www.elsevier.nl/locate/nimb
Radiation induced nucleation of nanoparticles in silica q D. Ila a
a,*
, E.K. Williams a, R.L. Zimmerman a, D.B. Poker b, D.K. Hensley
b
Department of Naur. and Phys. Sciences, Center for Irradiation of Materials, Alabama A&M University, P.O. Box 1447, Normal, AL 35762-1447, USA b Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Abstract There is a threshold implantation dose, after which some of the implanted species will tend to spontaneously form nanoclusters, over-dose-implantation. Similarly, there is a threshold implantation dose for the implanted species in a layer of the host material, such that after high temperature annealing the nanoclusters can nucleate before the implanted material can dissolve in the host material (during such heat treatments). In this paper, we present the results of our investigation of producing nanoclusters of gold in silica at ¯uences of two orders of magnitude less than what is traditionally used. This is accomplished by implanting 2.0 MeV Au into silica followed by MeV bombardment by MeV Si ions. This process was used to reduce the threshold implantation dose by at least two orders of magnitude. To follow the formation of nanoclusters, we used both indirect measurement methods such as optical absorption spectrophotometry (non-destructive), and direct methods such as transmission electron microscopy (destructive). The size of the nanoclusters, ranging from 1 to 10 nm, are controlled by the implantation dose and by the total electronic energy deposited by each post-bombarding ion in the implanted layer. We will show how and at what concentrations species such as gold nucleates to form nanoclusters, either by induced strain or by radiation-enhanced nucleation at a dose below that needed for spontaneous nanocluster formation. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 61.72. Ww; 61.82.Rx; 42.70.Nq Keywords: Ion implantation; Nanocrystals; Optical materials
1. Introduction
q Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and the Division of Materials Sciences, US Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp. * Corresponding author. Tel.: +1-256-851-5866; fax +1-256851-5868. E-mail address: [email protected] (D. Ila).
The production of the variety of optical devices relied mostly on changes in both the linear and nonlinear properties of glasses. The traditional technique to change the linear properties of glasses has been mostly by melting selected metals with glass, cooling the melt to form homogeneous glass, and then forming the metal colloids by a reheating process. Recently, metallic ion implantation in addition to thermal annealing has been used to
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 7 9 4 - 6
846
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
introduce similar eects near the surface as well as nonlinear optical properties [1±8]. The techniques used to form nanoclusters may be categorized as follows: 1. room temperature implantation followed by high temperature annealing; 2. room temperature implantation at dosage above the threshold dose for spontaneous nanocluster formation; 3. ion implantation at elevated temperatures. An attractive property of ion implantation is that the ions can be focused to introduce the linear and nonlinear properties in a well-de®ned space in an optical device. In all of the above cases, to produce nanoclusters of implanted ions such as gold in a medium such as silica, the implantations were done at high doses, from 1 to 2 ´ 1017 ions/cm2 , to overcome the solubility of the implanted species into the substrate. That is also why there is a wide distribution of cluster sizes produced by the above techniques. To overcome this problem, since 1994, we initiated a series of investigations into how to con®ne the implanted ions in a narrow layer, by generating chemical barriers, engineering defect barriers on both sides of the implanted layer, as well as combining two nonequilibrium processes, ion implantation and post-irradiation [9,10]. The latter technique, the focus of this paper, has been a combination of implantation of metallic species at room temperature, followed by room temperature bombardment by mega-electron-volt ions. The result has been the production of nanoclusters of gold in silica at ¯uences as low as 5 ´ 1015 / cm2 , a ®ne control in the size of the nanoclusters, and production of more uniform size nanoclusters. In this paper, we report on the synthesis of Au nanoclusters in silica (Suprasil 300) by combining two nonequilibrium techniques, consisting of implantation of 2.0 MeV Au and post-implantation bombardment with a 5.0 MeV Si beam. The formation of Au nanoclusters was investigated using optical absorption photospectrometry (OAP) techniques, following the formation of optical absorption bands due to formation of Au nanocrystals. The structure, shape, size and location of these nanoclusters were studied using cross-sec-
tional transmission electron spectroscopy (TEM) as well as electron diraction. 2. Experimental procedures The silica glass used is suprasil-300 of known purity, 5 ´ 5 ´ 0.5 mm3 , a commercial product of Heraeus Amersil, Gold ions at 2.0 MeV were implanted at low current density of 2 lA/cm2 to produce a Au implanted layer at concentrations between 5 ´ 1015 /cm2 and 1.2 ´ 1017 /cm2 . The beam current was maintained low to avoid the premature formation of gold clusters due to the ion beam heating. The depth of the implanted layer, 0.48 lm, as well as the penetration range of the postbombarding particles were calculated using the TRIM [11] computer code and measured using the RBS technique. The energy of the bombarding Si particles, 5.0 MeV, was selected such that Si ions stop outside the range of the Au implanted layer and at ¯uences between 6 1016 /cm2 and 2 1017 / cm2 . In all of the above post-implantation bombardments the temperature of the suprasil was kept at room temperature, 300 K. The OAP for small nanoclusters formed due to ultra-low dose implantation was measured by subtracting the OAP for Si bombarded suprasil and the OAP for Au implanted suprasil. This was done using two techiques: (1) during the OAP measurement of the Au implanted and then Si bombarded suprasil, (2) after the OAP measurements were done for Au implanted and then Si bombarded suprasil, for Si bombarded suprasil, and for Au implanted suprasil, then subtracting the normalized spectra for Si bombarded and Au implanted from the OAP spectrum for Au implanted and Si bombarded suprasil. Both of these techniques produce similar results. 3. Results and discussion The higher the ion beam ¯uence and the higher the atomic number of the bombarding ion the more the damage to the silica glass resulting in a change of the optical properties [7,12,13]. This was observed by absorption spectrometry during all
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
847
Fig. 1. From left to right, TEM micrographs of suprasil implanted at room temperature with (A) 2.0 MeV Au at 1:2 1017 =cm2 then annealed at 1173 K, the line on the top is the surface of the suprasil, (B) 2.0 MeV Au implanted suprasil at 6 1016 =cm2 then bombarded by 5.0 MeV Si at 6 1016 =cm2 , the image is taken from the implanted layer, (C) 2.0 MeV Au implanted suprasil at 5 1015 =cm2 then bombarded by 5.0 MeV Si at 6 1016 =cm2 , the image is from the implanted layer.
bombardments, but these eects are reduced with heat treatments above 970 K [7,8]. Fig. 1, from left to right, shows comparison of TEM micrographs of suprasil implanted at room temperature with 2.0 MeV Au at 1:2 1017 /cm2 then annealed at 1173 K with a 2.0 MeV Au implanted suprasil at 6 1016 /cm2 then bombarded by 5.0 MeV Si at 6 1016 /cm2 and the far right micrograph is the Au implanted suprasil at 5 1015 /cm2 then bombarded by 5.0 MeV Si at 6 1016 /cm2 . The 1173 K annealed Au implanted suprasil shows various size Au nanoclusters spread from the implantation range towards the surface. The micrographs from the post-implantation Si bombarded Au implanted suprasil show almost uniform size Au nanoclussters. The middle micrograph shows 2±3 nm size Au nanoclusters for 2.0 MeV Au implanted suprasil at 6 1016 /cm2 . The right micrograph shows sub-nanometer size Au nanoclusters 2.0 MeV Au implanted suprasil at 5 1015 /cm2 . Fig. 2 shows the optical absorption spectra bands for the 2.0 MeV Au implanted suprasil at 6 1016 /cm2 after bombardment by 5 Mev Si at 6 1016 /cm2 , 8 1016 /cm2 , 1 1017 /cm2 , and 2 1017 /cm2 at room temperature. As it is shown in this ®gure, the more the post-implanatation Si bombardment does the more pronounced the observed optical absorption band at about the cal-
Fig. 2. The optical absorption spectra of four suprasil samples ®rst implanted with 2.0 MeV Au at a ¯uence of 6 1016 =cm2 then each bombarded by 5 MeV Si at the ¯uences shown at room temperature.
culated wavelength using the Mie theory [14], 520 nm. The further post-implantation bombardment at room temperature, 2 1017 /cm2 , increases the
848
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
absorption coecient at higher Si implantation dose [15], as indicated by an increase in the background, considering the absorption due to implanted Si as background base line in this optical measurement. Fig. 3 shows the optical absorption spectra band from suprasil implanted with 1:2 1017 /cm2 Au at 2.0 Mev after annealing at 1273 K as well as suprasil implanted with 6 1016 /cm2 Au at 2.0 Mev and post-bombarded by 5.0 Mev Si at 6 1016 /cm2 , 8 1016 /cm2 , 1 1017 /cm2 , and 2 1017 /cm2 all were annealed at 1273 K. Comparing the absorption spectra band due to formation of Au nanoclusters obtained from heat treated Au implanted silica, 525 nm, and the absorption band due to Au nanoclusters, 517±520 nm, for post-implantation Si bombarded silica indicates 5±10 nm blue-shift which could be due to the change in the linear optical properties of the Si bombarded silica. Even after heat treatment at 1273 K the intensity of the absorption band for Si bombarded samples are similar to those from Fig. 2. The only dierence is the position of the ab-
Fig. 3. The optical absorption spectra for ®ve 1273 K annealed suprasil samples, one implanted with 1:2 1017 =cm2 Au only and the four Si bombarded samples shown in Fig. 2.
Fig. 4. The optical absorption band for 2.0 MeV Au implanted at 5 1015 =cm2 and then bombarded by 5.0 MeV Si at 6 1016 =cm2 at room temperature.
sorption band is slightly red shifted, which is due to thermal relaxation of the Si bombarded suprasil, thus recovering its original index of refraction value. Fig. 4 shows the optical absorption spectra bands for the 2.0 Mev Au implanted suprasil at 5 1015 /cm2 samples after bombardment by 5 Mev Si at 6 1016 /cm2 at room temperature. This ®gure corresponds to the far right TEM micrograph in Fig. 1 and is obtained by a background base-line subtraction of linear optical eect due to Si bombardment as well as due to Au implantation before Si bombardment. Table 1 shows the energy deposited by the electronic excitations (ee ), by nuclear stopping (en ), and integral of the product of the extinction coef®cient and the wavelength [10,14] at the absorption band after post-implantation bombardment by Si beam at 1.2, 2.0, and 5.0 MeV. The energy deposited at the Au implanted layer is calculated using TRIM computer code [11]. In this table the ex-
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850 Table 1 Energy deposited in the gold implanted layer and the product of extinction coecient and the wavelength for each incident energy Si beam energy (MeV)
DE (eV) due to ee
DE (eV) due to em
ak (nm)
1.2 2 5
107 017 176 868 373 018
6976 4814 2980
4.1 8.6 27
tinction coecient (a) is normalized and arbitrary unit. To evaluate the mechanism by which the nanoclusters are formed using post-implantation bombardment, we implanted gold and silicon at energies such that their implantation range were the same. We implanted 5.5 MeV Au ions at similar concentrations as above, 1.4 um implantation range, followed by 1.0 MeV Si ion bombardment at various ¯uences, 1.4 um implantation range produced no Au nanocluster. This recon®rms that the process of nanocluster formation is mostly due to the electronic energy deposited by the MeV Si ions passing through the Au implanted layer and not due to the nuclear stopping eects.
849
better control in their size distribution at much lower implantation dosage is to combine the ion implantation with a post-mega-electron-volt ion bombardment. The combined two nonequilibrium techniques can induce the formation of Au nanoclusters with ®ne control on the size of the nanoclusters, ranging from 0.5 to several nanometers depending on the combination of implanted dosage and the electronic energy deposited per postimplantation bombarding ions, thus generating an optical absorption band at about 520 nm and third order nonlinearity in a more con®ned volume.
Acknowledgements This project was supported by the Center for Irradiation of Materials at Alabama A&M University and Alabama EPSCoR-NSF Grant No. OSR-9559480. The work at ORNL was sponsored by the Division of Material Sciences, US Department of Energy, under Contract DE-ACO596OR22464 with Lockheed Martin Energy Research Corp.
References 4. Conclusion Comparing the area under the absorption band for constant ¯uence Si bombardment at dierent energies to the electronic energy deposited at the Au implanted depth, indicates similar increasing trend. Meanwhile, the energy deposited due to the nuclear stopping power of Si ions at dierent energies, in the Au implanted layer, shows just the opposite trend. The energy deposited by electronic excitations by MeV Si in the Au implanted layer contributes to both formation of large size nanoclusters and to an increase of the nanoclusterÕs volume fraction. That is, why the integral under the absorption band is increasing faster than the increase in the electronic energy deposited by Si ions at higher energies. The solution to produce a more con®ned metallic nanoclusters in any host material with a
[1] G.W. Arnold, J. Appl. Phys. 46 (1975) 4466. [2] G.W. Arnold, J.A. Bordes, J. Appl. Phys. 48 (1977) 1488. [3] R.H. Margruder III, R.A. Zuhr, D.H. Osborne Jr, Nucl. Instr. and Meth. B 99 (1995) 590. [4] R.F. Haglund Jr., D.H. Osborne Jr., R.H. Magruder III, C.W. White, R.A. Zuhr, P.D. Townsend, D.E. Hole, R.E. Leuchtner, Mat. Res. Soc. Symp. Proc. 354 (1995) 629. [5] C.W. White, D.S. Zhou, J.D. Budai, R.A. Zuhr, R.H. Magruder, D.H. Osborne, Mat. Res. Soc. Symp. Proc. 316 (1994) 499. [6] K. Fukumi, A. Chayahara, M. Adachi, K. Kadono, T. Sakaguchi, M. Miya, Y. Horino, N. Kitamura, J. Hayakawa, H. Yamashita, K. Fujii, M. Satou, Mat. Res. Soc. Symp. Proc. 235 (1992) 389. [7] D. Ila, Z. Wu, R.L. Zimmerman, S. Sarkisov, C.C. Smith, D.B. Poker, D.K. Hensley, Mat. Res. Soc. Symp. Proc. 457 (1997) 143. [8] D. Ila, E.K. Williams, S. Sarkisov, C.C. Smith, D.B. Poker, D.K. Hensley, Nucl. Instr. and Meth. B 141 (1998) 289.
850
D. Ila et al. / Nucl. Instr. and Meth. in Phys. Res. B 166±167 (2000) 845±850
[9] D. Ila, Z. Wu, C.C. Smith, D.B. Poker, D.K. Hensley, C. Klatt, S. Kalbitzer, Nucl. Instr. and Meth. B 127 (1997) 570. [10] D. Ila, E.K. Williams, C.C. Smith, D.B. Poker, D.K. Hensley, C. Klatt, S. Kalbitzer, Nucl. Instr. and Meth B 148 (1999) 1012. [11] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985.
[12] E.R. Schineller, R.P. Flam, D.W. Wilmot, J. Opt. Soc. Am. 58 (1968) 1171. [13] P.D. Townsend, Nucl. Instr. and Meth. B 46 (1990) 18. [14] G. Mie, Ann. Physik. 25 (1908) 377. [15] M. Verhaegen, L.B. Allard, J.L. Brebner, M. Essid, S. Roorda, J. Albert, Nucl. Instr. and Meth. B 106 (1995) 438.